Soil moisture indicating gage



March 27, 1962 R. MATSON SOIL MOISTURE INDICATING GAGE Filed Dec. 15, 1959 IN VENTOR R ANDOLPH MA rsolv ATTORNEY United States Patent 3,026,718 SOIL MOISTURE INDICATHNG GAGE Randolph Matson, 1954 Camino Lomo Verde, Vista, Calif. Filed Dec. 15, 1959, Ser. No. 859,680 2 Claims. (Cl. 73-73) This invention relates to a soil moisture indicating and measuring device and more particularly to such a device which is adapted to be inserted within the ground adjacent the roots of plants or the like, wherein an indication will be seen as to the moisture content of the soil.

The present invention is an improvement over my former Patent No. 2,801,538 granted August 6, 1957.

One of the important improvements in this application over the former patent is that the lower end of the gage, including a ceramic cup, is covered and sealed with a wax coating whereby water within the gage will not be dissipated through the porous end of the gage.

A further improvement of the present invention is that the sealed joint between the ceramic cup and the plastic tube is sealed as by a suitable epoxy adhesive and sealing material.

A further object of the invention and improvement over the above patent is the manner in which the indicating liquid is mounted within the indicating tube, the indicating liquid is deposited within a sack or envelope which is made of a material which will not permit osmosis between the water contained within the indicating tube and the indicating liquid containing sack.

A further object of the invention is to provide a threaded cap or plug for the gage, said cap or plug being provided with an enlarged lower portion to displace air which may be trapped in the water and which is further provided with O-ring for sealing the upper end of the gage.

The invention is illustrated in the accompanying drawings, wherein:

FIG. 1 is an elevation view of the gage;

FIG. 2 is a section on the line 22 of FIG. 1;

FIG. 3 is a section on the line 3-3 of FIG. 1; and

FIG. 4 is a section on the line 4-4 of FIG. 1.

The invention is illustrated in the accompanying drawings in which like numerals have been used to indicate similar parts throughout the various views and in which the gage includes an indicating or outer tube 6 of a plastic material, such as acrylic. The lower end of the plastic tube 6 has secured thereto a ceramic cup 7 having the upper part thereof adjacent its outer surface ground out to provide a recess 8, the tube 6 likewise along its outer portion adjacent the joint with the ceramic cup is ground out to provide a recess or channel 9. This formed re cess between the cup and the tube is preferably filled with an epoxy adhesive 10, of which there are many. During the process of making the gage, the epoxy adhesive is applied within the recessed joints 8 and 9 and the adhesive is scraped off flush with the outer surface of the tube 6 and ceramic cup 7. In manufacture, a polyethylene tape or the like is wrapped around the joint and around the epoxy adhesive to hold the adhesive in place while the same is drying or setting up, after which the polyethylene tape is removed to leave a neat joint between the plastic tube and the ceramic cup.

Positioned around the entire surface of the ceramic cup and extending above the joint between the tube and the cup is a coating of wax 12 which is of sufficient thickness to prevent the escape of moisture from the ceramic cup 7 to the atmosphere, or from the atmosphere into the cup. The wax covering at its upper end is tapered at 13 to gradually merge with the surface of the tube.

The acrylic tube 6 has at its upper end and secured thereto as by an epoxy adhesive a metallic or other aazan's Patented Mar. 27, 1962 material ring 14. This ring is provided on its inner surface With threads 15 which threads are adapted to receive the threaded portion 16 of a cap or plug type member 17. The upper end of the ring 14 is provided with a chamfered surface 13 which seats an O-ring 19 between the chamfered surface 18 and the underside 2%) of the cap 17. Of course, this O-ring is placed in this position to prevent leakage or seepage of water past the same and out of the gage. The lower end of the cap or plug 17 is provided with an enlarged extension or plug 21 which extends downwardly into the upper portion of the tube 6 and serves the function of preventing air from forming within the space above the tube 6 when the latter is filled to capacity with water. it has been found that if any air is trapped within the water column, this will affect the accuracy of the gage.

The inside of the tube is provided with an adjustable scale 22, said scale being graduated in hundredths of an atmosphere or bar and indicating dry and wet degrees and the same being frictionally held within the tube and which is capable of movement up and down as by a simple hooked-end wire which may be passed down within the tube when the cap 17 is removed to vary the position of the scale 22, as is necessary or desirable.

The gage is provided internally with a relatively small tube 23 adapted to receive an indicating fluid which will register with the marked scale and thereby indicate the moisture condition of the soil when the gage is being used. This indicating fluid containing tube is preferably formed of glass. The indicating tube 23 is sealed at its upper end and terminates in an enlarged bulb-like portion 24, such bulb-like portion being of suitable volume to contain a volume of trapped air above the indicating liquid. A rubber sleeve or cap member 25 frictionally engages the outer surface of the bulb-like portion 24 and thereby retains the tube 23 in position Within the gage. The upper end of the rubber sleeve 25 is provided with a horizontal bore and the sleeve has affixed thereto and extending horizontally therefrom and registering with the bore, a pair of tubular members 26, also made of rubber or other flexible material. The members 26 have positioned therein a metallic pin 27 which also extends through the bore of the cap 25, which pin 27 tends to hold the ends of the tube 26 in frictional engagement with the inner surface of the large tube 6, and thereby centers the indicating fluid containing tube 23 within the tube 6 in addition to anchoring the tube 23 therein.

The indicating tube 23 terminates adjacent its lower portion in a reduced tapered part 28, which has a small opening therein to restrict the speed of movement of the column. Adhesively secured to the tube 23, at a point slightly above the portion where it starts to taper to its reduced diameter, is a sack or container 29, said sack or container being formed of a material known in the trade as Kel-F, which is a synthetic plastic of trifluorochloroethylene which material is capable of heat sealing and further is of zero moisture absorption properties. In view of the fact that the indicating fluid containing sack 29 is made of a material of zero moisture absorption, it follows that the colored indicating fluid contained within the sack will not be diluted with water by osmosis causing failure of the calibration and distention of the sack 29. Further, with such an arrangement, it has been found possible to fill the gages with water at the point of distribution without the possibility of the instrument malfunctioning because water has entered the sack 29 as by the action of osmosis.

In the use of the device, a hole is formed in the ground surface where it is desired to use the gage, the hole being formed as by a pointed instrument which may be driven into the ground and which is sufficiently large to produce a hole in which the gage will be positioned after the tool has been removed therefrom, the hole preferably extending to the vicinity of the roots of the plants or the like where it is desired to determine the moisture content of the soil.

After the wax coating has been stripped from the porous or ceramic cup, the gage is deposited into the hole in the ground. If the ground adjacent to the porous cup is relatively wet, moisture will seep through the porous cup and thereby build up a pressure on the water Within the outer tube, which pressure will be transmitted to the sides of the indicating fluid containing sack 29 which pressure thereon will cause the indicating fluid within the sack to move up the inside of the indicating tube and a reading on the graduated scale can be seen, determined by the top of the column of the indicating fluid with respect to the graduated plate or scale. In the event that the ground is relatively dry, water or a certain amount of moisture will move from the outer tube through the porous cup in which event pressure on the sack 29 will be reduced to a certain extent wherein the indicating fluid within the indicating tube will drop, and reading the same against the graduated scale will indicate that the soil is dry. Under these conditions, water can be added to the soil until the gage indicates that water has penetrated to the depth of the porous cup when the column will return to 0. Water may then be withheld until the gage indicates that more water is needed to produce the best moisture soil condition for proper growing of the planted crops, flowers or the like.

It will be seen that the scale 22 may be readily adjusted to the zero position by moving the scale, which is frictionally fitted within the side of the outer tube. The zero adjustment is particularly important on long tensiometers where the hydrostatic effect of the column of water becomes appreciable. The tension at the porous or ceramic cup is shown correctly when the reading is zero while the cup is immersed in water. When, for example, a thirty inch instrument is adjusted in this manner, the column will extend about one-eighth of an inch above the zero position when the plug or cap 17 is removed.

It will be seen that in the present form of the invention, the lower ceramic cup portion thereof is covered with a wax or other sealing material and, of course, before the instrument is used, this ,wax coating must be stripped from the ceramic cup to permit ingress and egress of moisture into and out of the gage. With the ceramic cup coated with a wax-like solution, moisture is prevented from passing through the ceramic cup and it has been found that the gage can be distributed and shipped full of degassed water and consequently, when the consumer receives the same, it is only necessary to remove the wax coating and insert the gage in the ground. Further, because the sack 29 is made of plastic trifluorochloroethylene, it prevents osmosis between the indicating fluid and the water within the tube, as it has heretofore been found that there was some possibility of the water entering the indicating fluid by osmosis and cansing malfunction and distention of the sack of the former patent. However, it has been found that with the indicating fluid contained in sack 29, such transfer of water to the indicating fluid within the gage is prevented. Thus, it will be seen that the gages can be shipped full of water and can be used forthwith.

It is not intended that the invention be limited to the exact construction shown but is capable of modification and variation within the scope of the following claims.

I claim:

1. In a soil moisture indicating gage including a transparent nonporous tubular casing member, a cup-shaped porous ceramic bulb portion disposed on one end of said casing and a closure member disposed on the opposite end, the combination comprising an elongated moisture indicating tube including a flexible fluid reservoir on the lower end thereof, said tube and said reservoir being disposed within said transparent casing member, support means for supporting said indicating tube and reservoir axially of said casing, said support including a downwardly extending resilient sleeve member adapted to frictionally engage the outer surface of the upper end portion of said indicating tube for supporting the same within the tube, a plurality of outwardly directed tubular arms extending radially outwardly from said resilient sleeve, said arms extending outwardly a suitable distance to frictionally engage the inner walls of said tubular casing, arm stiffening means in the form of a rigid pin disposed with in said outwardly directed tubular arms and terminating at a point adjacent the extremity of said tubular arm members to render said arms substantially rigid and to support the extremities of the arms in frictional engagement with the inner wall of said casing whereby to preclude unintended relative movement of said indicating tube and said casing, substantially U-shaped scale means frictionally disposed within said casing and partially encircling said indicating tube, said scale adapted for longitudinal movement within said casing relative to both said casing and said indicating tube for calibrating said gage.

2. In a soil moisture indicating gage including a transparent nonporous tubular casing member, a cup-shaped porous ceramic bulb portion disposed on one end of said casing and a closure member disposed on the opposite end, the combination comprising an elongated moisture indicating tube including a flexible fluid reservoir on the lower end thereof, said tube and said reservoir being disposed within said transparent casing member, support means for supporting said indicating tube and reservoir axially of said casing, said support including a downwardly extending resilient sleeve member adapted to frictionally engage the outer surface of the upper end portion of said indicating tube for supporting the same within the tube, means defining a bore extending through said sleeve adjacent the upper end thereof, a transverse resilient tube extending through said bore and engaging the inner walls of said casing, a rigid pin disposed within said transverse tube for stiffening the same whereby said indicating tube and said flexible reservoir are pivotally suspended axially within said casing, and a substantially U-shaped scale means frictionally disposed within said casing and partially encircling said indicating tube, said scale adapted for longitudinal movement within said casing relative to both said casing and said indicating tube for calibrating said gage.

References Cited in the file of this patent UNITED STATES PATENTS 2,801,538 Matson Aug. 6, 1957 2,878,671 Prosser et al. Mar. 24, 1959 FOREIGN PATENTS 444,330 Great Britain Mar. 19, 1936 

